Universe’s star-making occurred earlier than once thought, suggests ALMA
ALMA has not only found that star formation sprang into life earlier than once thought, it has also excitingly locked down the most distant detection of water.
Energetic bursts of star birth occurred a full one billion years earlier than once suspected according to new observations returned by the Atacama Large Millimeter/submillimeter Array (ALMA). What’s more, the observatory, which was recently officially opened for scientific business on Wednesday 13 March, has also pinpointed the most distant observation of water in the cosmos to date.
The vigorous production of new stars is believed to have occurred back in the Universe’s early times where stunningly bright galaxies of epic proportions were commonplace in the young fabric of space. These structures, aptly named starburst galaxies, are reminiscent of factories, converting their supplies of gas and dust into fresh young stars at an incredible rate. Now scientists using ALMA have identified a treasure trove of starburst galaxies that existed back when the Universe was young.
These ancient relics were initially pinpointed using the US National Science Foundation’s 10-metre South Pole Telescope (SPT) before the help of the unrivaled sensitivity of ALMA was enlisted to capture their galactic light. The research was conducted using just 16 of ALMA’s 66 antennas because at the time of the observations the observatory was not complete. Hezaveh’s team, led by the California Institute of Technology’s Joaquin Vieira, was able to look at different stages of the Universe’s 13.7 billion year history. The international team of scientists, which also includes Axel Weiss from the Max-Planck-Institut fur Radioastronomie in Germany, were amazed to find that many of these dusty star-forming galaxies are even further away than they anticipated, with a baby stellar boom taking place 12 billion years ago when the Universe was at a comparatively 2 billion years old – a whole billion years earlier than once thought.
“Some of these galaxies form more than 4000 stars like our Sun per year. This is a very fast rate of star formation,” comments Yashar Hezaveh of McGill University in Canada, who led part of the study. “For comparison, spiral galaxies like the Milky Way on average form about one star per year. Such a fast star formation rate, if sustained, means that a whole population of stars in a galaxy could form over very short timescales – a few hundred million years, which astronomically is a very very short timescale.”
Of course, where there are shiny bright stars, there is also luminescence. This light is thrown out into space and, since these ancient galaxies are so distant, it takes some billions of years to reach us, acting as a timeline between our present and the Universe’s past as we peer into the cosmos‘ youth. “If galaxies are at different distances to us, each of them shows the image of the galaxy at a different time in the history of the Universe.” adds Hezaveh. “So if I have 100 galaxies with a range of distances, I am actually looking at 100 different times in the history of the Universe. In fact I will have 100 snapshots of different galaxies at 100 different times in the history of the Universe.”
“We have used a method to select galaxies independent of distance,” Joaquin Vieira tells All About Space. “We have measured the distances to those galaxies by observing light emitted from carbon monoxide.” Starburst galaxies are notorious for emitting great amounts of infrared light that radiate from the great heat and energy involved in explosions of new stars. The carbon monoxide that can be found in these galaxies emits in the millimetre and submillimetre wavelengths. “By measuring the distances to all of these galaxies we can reconstruct their evolutionary history. It turns out that they formed much earlier in the Universe than we previously thought – just 1 billion years after the Big Bang,” adds Vieira.
Out of the 26 galaxies that ALMA had in its sights, two galaxies were found to be the most distant of their star-making kind. Astonishingly water molecules were also found in one of these faraway galaxies, marking not just the furthest water has been detected, but also a double whammy in the team’s scientific results. “Water exists in galaxies one billion years after the Big Bang and probably even before that,” says Vieira. “In one particular galaxy in which we observed water, we think that it indicates the presence of a supermassive black hole at its centre.”
According to Hezaveh water is actually a common molecule in the Universe and detecting it is a question of quantum mechanics. “Different chemical compositions, when heated, emit light at very specific wavelengths characteristic of that chemical molecule,” he explains. “This serves as a unique fingerprint of each molecule.” Observing an increase in radiation at a frequency characteristic of a given chemical compound, the researchers were able to detect the water as well as the previously mentioned carbon monoxide littering these galaxies. “The existence of these molecules in large quantities in these star forming galaxies can help us understand the role of chemical compositions in the birth and evolution of galaxies.”
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Images courtesy of ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh and C. Padilla